1. Field of the Invention
The invention is directed to an improved actuator for a control unit.
2. Description of the Prior Art
In a known actuator for a throttle valve in the intake stub of an internal combustion engine (German Patent Disclosure DE 196 12 869 A1), the step-up gear disposed between the motor power takeoff shaft and the control shaft is a two-stage spur pinion gear with an intermediate wheel, which with a first toothed portion meshes with a motor pinion seated on the motor power takeoff shaft and with a second toothed portion meshes with a driving gear wheel fixedly disposed on the control shaft. The driving gear wheel and the control shaft are supported rotatably in an actuator housing that receives the control motor and the step-up gear. A restoring device assures that if the control motor fails, the throttle valve is restored to a basic position, in which only emergency operation of the engine is possible. The restoring device has a torsion spring, concentrically surrounding the control shaft and embodied as a cylindrical helical spring, and a stop piece that is received rotationally movably on the control shaft. With one spring end, the torsion spring engages the driving gear wheel, and with its other spring end it engages the stop piece and is braced axially between the driving gear wheel and the stop piece, and the stop piece in turn is braced axially on the rotary bearing, received fixedly in the actuator housing, for the control shaft. Via its spring ends, the torsion spring exerts torque on the driving gear wheel and the stop piece, and the stop piece in turn cooperates, via a stop disposed on it, with a counterpart stop disposed on the intermediate wheel. This restoring torque increases with increasing rotation of the throttle valve out of its basic position. If the control motor fails, this restoring torque rotates the throttle valve back to its basic position.
In an actuator for adjusting a throttle device in an internal combustion engine known from German Patent Disclosure DE 40 39 728 A1, the step-up gear between the motor power takeoff shaft and the control shaft is embodied as a worm gear with a worm and a circular-arclike toothed strip. The worm is disposed on the motor power takeoff shaft in a manner fixed against relative rotation, and the toothed strip is guided displaceably in the actuator housing along a circular arc. A driver arm is fixedly disposed on the control shaft and rests with one end of the arm on the face end of the toothed strip. A spiral spring seated on the control shaft presses the driver arm against the toothed segment by nonpositive engagement, so that the drive arm upon displacement of the toothed strip is pivoted and thus the control shaft with the control unit is rotated.